Move macro_rules! macros to libstd

They all have to go into a single module at the moment unfortunately.
Ideally, the logging macros would live in std::logging, condition! would
live in std::condition, format! in std::fmt, etc. However, this
introduces cyclic dependencies between those modules and the macros they
use which the current expansion system can't deal with. We may be able
to get around this by changing the expansion phase to a two-pass system
but that's for a later PR.

Closes #2247
cc #11763
Delete ignore! macro

This was a holdover from when we didn't allow nested comment blocks
(think #if 0). It isn't used anywhere.
auto merge of #11774 : sfackler/rust/move-macros, r=pcwalton

They all have to go into a single module at the moment unfortunately.
Ideally, the logging macros would live in std::logging, condition! would
live in std::condition, format! in std::fmt, etc. However, this
introduces cyclic dependencies between those modules and the macros they
use which the current expansion system can't deal with. We may be able
to get around this by changing the expansion phase to a two-pass system
but that's for a later PR.

Closes #2247
cc #11763